Inertial sensor

ABSTRACT

An inertial sensor includes a base portion, a weight portion, a connection portion, and a first sensing element unit. The connection portion connects the weight portion and the base portion and is capable of being deformed in accordance with a change in relative position of the weight portion with respect to the position of the base portion. The first sensing element unit is provided on a first portion of the connection portion and includes a first magnetic layer, a second magnetic layer, and a nonmagnetic first intermediate layer. The nonmagnetic first intermediate layer is provided between the first magnetic layer and the second magnetic layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 14/460,450, filed Aug. 15,2014, which is incorporated herein by reference.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2013-196056, filed on Sep. 20, 2013; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an inertial sensor.

BACKGROUND

There is an inertial sensor using MEMS (micro electro mechanicalsystems) technology of a piezoresistance type using silicon (Si), forexample. The inertial sensor can sense acceleration as well as inertia,for example. It is desired for the inertial sensor to increasesensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are schematic views showing an inertial sensoraccording to a first embodiment;

FIG. 2A and FIG. 2B are schematic cross-sectional views showing theinertial sensor according to the first embodiment;

FIG. 3A to FIG. 3C are schematic perspective views showing operations ofthe inertial sensor according to the first embodiment;

FIG. 4 is a schematic perspective view showing part of the inertialsensor according to the first embodiment;

FIG. 5A to FIG. 5I are graphs showing characteristics of inertialsensors;

FIG. 6A to FIG. 6I are graphs showing characteristics of inertialsensors;

FIG. 7A and FIG. 7B are graphs showing characteristics of inertialsensors;

FIG. 8A to FIG. 8D are microscope images showing characteristics of aninertial sensor;

FIG. 9A to FIG. 9D are microscope images showing characteristics of aninertial sensor;

FIG. 10 is a graph showing characteristics of an inertial sensor;

FIG. 11A and FIG. 11B are schematic perspective views showing part ofthe inertial sensor according to the first embodiment;

FIG. 12 is a schematic perspective view showing an inertial sensoraccording to a second embodiment;

FIG. 13A to FIG. 13C are schematic cross-sectional views showing theinertial sensor according to the second embodiment;

FIG. 14A and FIG. 14B are schematic plan views showing the inertialsensor according to the second embodiment;

FIG. 15A and FIG. 15B are schematic plan views showing other inertialsensors according to the second embodiment;

FIG. 16A and FIG. 16B are schematic perspective views showing aninertial sensor according to a third embodiment;

FIG. 17 is a schematic plan view showing the inertial sensor accordingto the third embodiment;

FIG. 18A and FIG. 18B are schematic plan views showing other inertialsensors according to the third embodiment;

FIG. 19 is a schematic perspective view showing another inertial sensoraccording to the third embodiment;

FIG. 20A and FIG. 20B are schematic perspective views showing anotherinertial sensor according to the third embodiment;

FIG. 21 is a schematic plan view showing another inertial sensoraccording to the third embodiment;

FIG. 22A and FIG. 22B are schematic plan views showing other inertialsensors according to the third embodiment;

FIG. 23 is a schematic perspective view showing an inertial sensoraccording to a fourth embodiment; and

FIG. 24A to FIG. 24C are schematic diagrams showing inertial sensorsaccording to the fourth embodiment.

DETAILED DESCRIPTION

According to one embodiment, an inertial sensor includes a base portion,a weight portion, a connection portion, and a first sensing elementunit. The connection portion connects the weight portion and the baseportion. The connection portion is configured to be deformed inaccordance with a change in a relative position of the weight portionwith respect to a position of the base portion. The first sensingelement unit is provided on a first portion of the connection portionand includes a first magnetic layer, a second magnetic layer, and anonmagnetic first intermediate layer. The nonmagnetic first intermediatelayer is provided between the first magnetic layer and the secondmagnetic layer.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

The drawings are schematic or conceptual; and the proportions of sizesamong portions, etc. are not necessarily the same as the actual valuesthereof. Further, the dimensions and proportions may be illustrateddifferently among drawings, even for identical portions.

In the specification of this application and the drawings, componentssimilar to those described in regard to a drawing thereinabove aremarked with the same reference numerals, and a detailed description isomitted as appropriate.

First Embodiment

FIG. 1A and FIG. 1B are schematic views illustrating an inertial sensoraccording to a first embodiment.

FIG. 1A is a schematic cross-sectional view illustrating the inertialsensor. FIG. 1B is a plan view illustrating the inertial sensor. Asshown in FIG. 1A and FIG. 1B, an inertial sensor 310 according to theembodiment includes a base portion 71, a weight portion 72, a connectionportion 74, and a sensing element unit 50 (a first sensing element unit50 a).

The connection portion 74 connects the weight portion 72 and the baseportion 71. The connection portion 74 is configured to be deformed inaccordance with the change in relative position of the weight portion 72with respect to the base portion 71. The connection portion 74 includesa first portion 74 a, for example.

The first sensing element unit 50 a is provided on the first portion 74a of the connection portion 74, for example. The first sensing elementunit 50 a is fixed to the first portion 74 a, for example. The firstsensing element unit 50 a includes a first magnetic layer 10 a, a secondmagnetic layer 20 a, and a first intermediate layer 30 a. The firstmagnetic layer 10 a is a first magnetization free layer 10, for example.The second magnetic layer 20 a is a reference layer 20. Also the secondmagnetic layer 20 a may be a magnetization free layer. The firstintermediate layer 30 a is an intermediate layer 30. The firstintermediate layer 30 a is provided between the first magnetic layer 10a and the second magnetic layer 20 a. The first intermediate layer 30 ais nonmagnetic, for example.

The first magnetic layer 10 a, the second magnetic layer 20 a, and thefirst intermediate layer 30 a are included in a resistance change unit(a first resistance change unit 50 sa), for example. In this example,the second magnetic layer 20 a is disposed between the first magneticlayer 10 a and the connection portion 74. In the embodiment, the firstmagnetic layer 10 a may be disposed between the second magnetic layer 20a and the connection portion 74.

In this example, the first sensing element unit 50 a further includes afirst electrode 51 a (for example, a lower-side electrode 51) and asecond electrode 52 a (for example, an upper-side electrode 52). Thefirst resistance change unit 50 sa is provided between the firstelectrode 51 a and the second electrode 52 a.

The first magnetic layer 10 a is disposed between the first electrode 51a and the second electrode 52 a, for example. The second magnetic layer20 a is disposed between the first magnetic layer 10 a and the firstelectrode 51 a. In this example, the first electrode 51 a is disposedbetween the second electrode 52 a and the connection portion 74. In theembodiment, the second electrode 52 a may be disposed between the firstelectrode 51 a and the connection portion 74.

The direction from the second magnetic layer 20 a toward the firstmagnetic layer 10 a is defined as the Z-axis direction (the stackingdirection). One direction perpendicular to the Z-axis direction isdefined as the X-axis direction. The direction perpendicular to theZ-axis direction and perpendicular to the X-axis direction is defined asthe Y-axis direction.

The lengths along the Z-axis direction of the first magnetic layer 10 a,the second magnetic layer 20 a, and the first intermediate layer 30 acorrespond to the thicknesses of the respective layers. The length alongthe Z-axis direction of the connection portion 74 corresponds to thethickness of the connection portion 74. The length along the Z-axisdirection of the base portion 71 corresponds to the thickness of thebase portion 71. The thickness along the Z-axis direction of the weightportion 72 corresponds to the thickness of the weight portion 72.

The length (thickness) of the connection portion 74 (the first portion74 a) is shorter (thinner) than the length (thickness) of the weightportion 72 in the direction from the base portion 71 toward the weightportion 72 (for example, the X-axis direction), for example. Asdescribed later, the length (width) of the connection portion 74 (thefirst portion 74 a) in a direction (the Y-axis direction) perpendicularto the direction from the base portion 71 toward the weight portion 72(for example, the X-axis direction) is shorter than the length in theX-axis direction of the connection portion 74, for example. Thereby,when the weight portion 72 has moved, the strain is large (for example,at the maximum), for example.

Thereby, the connection portion 74 is deformed more easily than theweight portion 72, for example. The connection portion 74 is deformed inaccordance with the change in position of the weight portion 72.

FIG. 2A and FIG. 2B are schematic cross-sectional views illustrating theinertial sensor according to the first embodiment.

FIG. 2A and FIG. 2B correspond to a first state ST1 and a second stateST2, respectively.

As shown in FIG. 2A, in the first state ST1, the relative position ofthe weight portion 72 with respect to the base portion 71 is a firstposition. The first state ST1 is a state where no acceleration (force)is applied to the weight portion 72, for example.

As shown in FIG. 2B, in the second state ST2, the relative position ofthe weight portion 72 with respect to the base portion 71 is a secondposition. The second position is different from the first position. Thesecond state ST2 is a state where an acceleration 72 g is applied to theweight portion 72, for example. The form of the connection portion 74(the first portion 74 a) in the second state ST2 is different from theform of the connection portion 74 (the first portion 74 a) in the firststate ST1. Thus, the connection portion 74 is deformed in accordancewith the change in relative position of the weight portion 72 withrespect to the base portion 71.

The base portion 71 is used by being fixed to a moving body, forexample, and the base portion 71 moves together with the body it isfixed to. On the other hand, the weight portion 72 is connected to thebase portion 71 via the connection portion 74 that can be warped or thelike. Thereby, the weight portion 72 can move differently from themovement of the base portion 71. When the base portion 71 has moved, theweight portion 72 does not move together with the base portion 71substantially, due to inertia, for example. A strain is generated in theconnection portion 74 connecting the base portion 71 and the weightportion 72, and the strain is sensed; thereby, at least one of theinertia and the acceleration is sensed.

The direction of the magnetization of the first magnetic layer 10 a canchange in conjunction with the deformation of the connection portion 74.Also the direction of the magnetization of the second magnetic layer 20a may change in conjunction with the deformation of the connectionportion 74.

In the case where the first magnetic layer 10 a is a magnetization freelayer and also the second magnetic layer 20 a is a magnetization freelayer, the directions of the magnetizations of both magnetic layerschange in conjunction with the deformation of the connection portion 74,for example. In the first state ST1, the magnetization of the firstmagnetic layer 10 a is in a first magnetization direction, and themagnetization of the second magnetic layer 20 a is in a secondmagnetization direction, for example. In the second state ST2, themagnetization of the first magnetic layer 10 a is in a directiondifferent from the first magnetization direction, and the magnetizationof the second magnetic layer 20 a is in a direction different from thesecond magnetization direction.

In the case where the first magnetic layer 10 a is a magnetization freelayer and the second magnetic layer 20 a is a magnetization fixed layer,the direction of the magnetization of the first magnetic layer 10 achanges in conjunction with the deformation of the connection portion74, for example. In the first state ST1, the magnetization of the firstmagnetic layer 10 a is in the first magnetization direction, and themagnetization of the second magnetic layer 20 a is in the secondmagnetization direction, for example. In the second state ST2, themagnetization of the first magnetic layer 10 a is in a directiondifferent from the first magnetization direction, and the magnetizationof the second magnetic layer 20 a is in the second magnetizationdirection.

Thus, the direction of the magnetization of the magnetic layer changeswith the deformation of the connection portion 74; thereby, theresistance of the current flowing through the first resistance changeunit 50 sa changes. In the inertial sensor 310, the position (relativeposition) of the weight portion 72 changes in accordance with theapplied acceleration 72 g. The connection portion 74 is deformed by theposition change, and the direction of the magnetization of the magneticlayer changes in conjunction with the deformation. The acceleration issensed by sensing the change in resistance in accordance with the changein direction of the magnetization of the magnetic layer. The change indirection of the magnetization is due to the inverse magnetostrictioneffect described later, and is obtained by utilizing the change inmagnetization direction of the magnetic layer when a strain is generatedin the magnetic layer in conjunction with the deformation.

Examples of the change in magnetization in the resistance change unit(the first resistance change unit 50 sa) and the change in resistancewill now be described. In the following, for easier description, adescription is given for the case where the second magnetic layer 20 ais a magnetization fixed layer and the first magnetic layer 10 a is amagnetization free layer. In the sensing element unit 50, “inversemagnetostriction effect” that ferromagnetic materials have and “MReffect” that is exhibited in the resistance change unit are utilized.

The “MR effect” is a phenomenon in which, in a stacked film including amagnetic material, the value of the electric resistance of the stackedfilm changes due to the change in magnetization of the magnetic materialwhen an external magnetic field is applied. The MR effect includes GMR(giant magnetoresistance) effect, TMR (tunneling magnetoresistance)effect, or the like, for example. The MR effect is exhibited by passinga current through the resistance change unit to read the change inrelative angle between the directions of the magnetizations as anelectric resistance change. Based on the stress applied to the sensingelement unit 50, a tensile stress is applied to the resistance changeunit, for example. At this time, the direction of the magnetization ofthe first magnetic layer 10 a changes in accordance with the magnitudeand direction of the stress. The value of the resistance accompanyingthe current passed through the magnetic layer changes in accordance withthe relative angle between the magnetization direction of the secondmagnetic layer 20 a and the magnetization direction of the firstmagnetic layer 10 a. When the resistance in the low resistance state isdenoted by R and the amount of change in electric resistance thatchanges due to the MR effect is denoted by ΔR, ΔR/R is referred to asthe “MR ratio.”

FIG. 3A to FIG. 3C are schematic perspective views illustratingoperations of the inertial sensor according to the first embodiment.

The drawings illustrate different states of the sensing element unit 50.The drawings illustrate relationships between the magnetizationdirection in the sensing element unit 50 and the direction of tensilestress.

FIG. 3A shows a state where no tensile stress is applied. At this time,in this example, the direction of the magnetization of the secondmagnetic layer 20 a (the reference layer 20) is the same as thedirection of the magnetization of the first magnetic layer 10 a (themagnetization free layer 10).

FIG. 3B shows a state where a tensile stress is applied. In thisexample, a tensile stress is applied along the X-axis direction. Thetensile stress along the X-axis direction is applied by the deformationof the connection portion 74, for example. That is, the tensile stressis applied in a direction orthogonal to the direction (in this example,the Y-axis direction) of the magnetization of the second magnetic layer20 a (the reference layer 20) and the first magnetic layer 10 a (themagnetization free layer 10). At this time, the magnetization of thefirst magnetic layer 10 a (the magnetization free layer 10) rotates soas to be the same direction as the direction of the tensile stress. Thisis referred to as “inverse magnetostriction effect.” At this time, themagnetization of the second magnetic layer 20 a (the reference layer 20)is fixed. By the rotation of the magnetization of the first magneticlayer 10 a (the magnetization free layer 10), the relative angle betweenthe direction of the magnetization of the second magnetic layer 20 a(the reference layer 20) and the direction of the magnetization of thefirst magnetic layer 10 a (the magnetization free layer 10) is changed.

In FIG. 3B, the magnetization direction of the second magnetic layer 20a (the reference layer 20) is shown as an example. The magnetizationdirection may not be the direction shown in FIG. 3B.

In the inverse magnetostriction effect, the easy axis of magnetizationvaries with the sign of the magnetostriction constant of a ferromagneticmaterial. In many materials exhibiting a large inverse magnetostrictioneffect, the magnetostriction constant has the plus sign. In the casewhere the magnetostriction constant is the plus sign, the direction inwhich a tensile stress is applied as described above is themagnetization easy axis. In other words, in the case where themagnetostriction constant is plus, the magnetization of the firstmagnetic layer 10 a (the magnetization free layer 10) rotates toward thedirection of the magnetization easy axis in which the tensile stress isapplied as mentioned above. On the other hand, in the case where themagnetostriction constant is the minus sign, a direction perpendicularto the direction in which the tensile stress is applied is themagnetization easy axis. In this case, due to the stress application,the magnetization direction of the first magnetic layer 10 a is directedto the direction perpendicular to the direction in which the stress isapplied.

In the case where the magnetostriction constant of the first magneticlayer 10 a (the magnetization free layer 10) is plus, the initialmagnetization direction of the first magnetic layer 10 a (themagnetization free layer 10) (the magnetization direction when no stressis applied) is set to a direction different from the direction in whichthe tensile stress is applied, for example. On the other hand, in thecase where the magnetostriction constant is minus, a directionperpendicular to the direction in which the tensile stress is applied isthe magnetization easy axis.

FIG. 3C illustrates a state where the magnetostriction constant isminus. In this case, the initial magnetization direction of the firstmagnetic layer 10 a (the magnetization free layer 10) (the magnetizationdirection when no stress is applied) is set to a direction differentfrom the directions perpendicular to the direction (in this example, theX-axis direction) in which the tensile stress is applied.

In FIG. 3C, the magnetization direction of the second magnetic layer 20a (the reference layer 20) is shown as an example. The magnetizationdirection may not be the direction shown in FIG. 3C.

The electric resistance of the sensing element unit 50 (the resistancechange unit) changes due to the MR effect in accordance with the anglebetween the magnetization of the first magnetic layer 10 a and themagnetization of the second magnetic layer 20 a, for example.

The magnetostriction constant (λs) represents the magnitude of thedeformation when an external magnetic field is applied and aferromagnetic layer is magnetically saturated in a certain direction.Assuming that the length of the ferromagnetic layer in a state wherethere is no external magnetic field is L, when the length of theferromagnetic layer has changed by ΔL when an external magnetic field isapplied, the magnetostriction constant λs is expressed by ΔL/L. Althoughthe amount of change varies with the magnitude of the magnetic field,the magnetostriction constant λs is expressed as ΔL/L in a state where asufficient magnetic field is applied and magnetization is saturated.

In the case where the second magnetic layer 20 a (the reference layer20) is a magnetization fixed layer, Fe, Co, Ni, or an alloy material ofthem is used for the second magnetic layer 20 a, for example.Furthermore, a material in which an additive element is added to thematerial mentioned above or the like is used for the second magneticlayer 20 a. CoFe alloy, CoFeB alloy, NiFe alloy, and the like may beused for the second magnetic layer 20 a, for example. The thickness ofthe second magnetic layer 20 a is not less than 2 nanometers (nm) andnot more than 6 nm, for example.

For the first intermediate layer 30 a, a metal or an insulator may beused. As the metal, Cu, Au, Ag, and the like may be used, for example.In the case of metals, the thickness of the first intermediate layer 30a is not less than 1 nm and not more than 7 nm, for example. As theinsulator, a magnesium oxide (MgO etc.), an aluminum oxide (Al₂O₃ etc.),a titanium oxide (TiO etc.), a zing oxide (ZnO etc.), or the like may beused, for example. In the case of insulators, the thickness of the firstintermediate layer 30 a is not less than 1 nm and not more than 3 nm,for example.

In the case where the first magnetic layer 10 a is a magnetization freelayer, at least one of Fe, Co, and Ni or an alloy material including atleast one of them is used for the first magnetic layer 10 a, forexample. A material in which an additive element is added to thematerial mentioned above is used.

For the first magnetic layer 10 a, a material with a largemagnetostriction (magnetostriction constant) is used. Specifically, amaterial of which the absolute value of the magnetostriction is largerthan 10⁻⁵ is used. Thereby, the magnetization changes sensitively withthe strain. For the first magnetic layer 10 a, either a material havinga positive magnetostriction or a material having a negativemagnetostriction may be used.

For the first magnetic layer 10 a, a single element metal of Fe, Co, orNi may be used, for example. For the first magnetic layer 10 a, an alloyincluding at least one of Fe, Co, and Ni may be used, for example. Otherthan them, for the first magnetic layer 10 a, Fe—Co—Si—B alloy, aTb-M-Fe alloy (M being Sm, Eu, Gd, Dy, Ho, or Er), a Tb-M1-Fe-M2 alloy(M1 being Sm, Eu, Gd, Dy, Ho, or Er; M2 being Ti, Cr, Mn, Co, Cu, Nb,Mo, W, or Ta), an Fe-M3-M4-B alloy (M3 being Ti, Cr, Mn, Co, Cu, Nb, Mo,W, or Ta; M4 being Ce, Pr, Nd, Sm, Tb, Dy, or Er), Ni, Al—Fe, a ferrite(Fe₃O₄, (FeCo)₃O₄, or the like), and the like may be used. In theTb-M-Fe alloy and the Fe-M3-M4-B alloy mentioned above, themagnetostriction constant λs is larger than 100 ppm. The thickness ofthe first magnetic layer 10 a is 2 nm or more, for example.

The first magnetic layer 10 a may have a two-layer structure. In thiscase, the first magnetic layer 10 a may include a layer of FeCo alloyand the following layer stacked with the layer of FeCo alloy. The layerof FeCo alloy is stacked with a layer of a material selected fromFe—Co—Si—B alloy, a Tb-M-Fe alloy (M being Sm, Eu, Gd, Dy, Ho, or Er), aTb-M1-Fe-M2 alloy (M1 being Sm, Eu, Gd, Dy, Ho, or Er; M2 being Ti, Cr,Mn, Co, Cu, Nb, Mo, W, or Ta), an Fe-M3-M4-B alloy (M3 being Ti, Cr, Mn,Co, Cu, Nb, Mo, W, or Ta; M4 being Ce, Pr, Nd, Sm, Tb, Dy, or Er), Ni,Al—Fe, a ferrite (Fe₃O₄, (FeCo)₃O₄, or the like), and the like. In theTb-M-Fe alloy and the Fe-M3-M4-B alloy mentioned above, themagnetostriction constant λs is larger than 100 ppm.

When the magnetostriction constant of the first magnetic layer 10 a islarge as mentioned above, a high strain sensitivity GF (gauge factor) isobtained. The value of the GF is greatly influenced by not only themagnetostriction constant but also the soft magnetic properties of thefirst magnetic layer 10 a. The strain sensitivity GF is expressed byGF=(dR/R)/Δε, where Δε is the strain, R is the resistance, and ΔR is thechange in resistance when a strain of Δε is given. The strainsensitivity GF represents the magnitude of the amount of resistancechange in a unit strain change, and is a dimensionless amount.

It is found that a material that is an alloy including Fe and has anamorphous structure has a large GF, for example. In this material, a GFvalue of 3,000 or more is obtained, for example.

In the specification of this application, the amorphous structureincludes microcrystalline structures. In microcrystalline structures,the size of the crystal grain is larger than 2 nm. The amorphousstructure further includes structures having crystal structure notfound. Microcrystalline structures or structures having crystalstructure not found can be observed by a real image obtained by atransmission electron microscope, for example. Furthermore, electrondiffraction using a microbeam in a magnetic layer may be used, forexample. Determination can be made by whether the electron diffractionpattern exhibits a spot pattern or a ring-like pattern, for example. Thespot pattern corresponds to a crystal structure, for example. Thering-like pattern corresponds to an amorphous structure. Examples of theelectron diffraction are described later.

The structure of the first magnetic layer 10 a is made amorphous byusing Fe including B (Boron) as the first magnetic layer 10 a, forexample. In the embodiment, a functional layer like the following may beprovided.

FIG. 4 is a schematic perspective view illustrating part of the inertialsensor according to the first embodiment.

As shown in FIG. 4, the first magnetic layer 10 a is disposed between afunctional layer 15 a and the first intermediate layer 30 a. Byproviding the functional layer 15 a, the concentration of B in the firstmagnetic layer 10 a can be increased. The first magnetic layer 10 a (forexample, a CoFeB layer, thickness: 4 nm) is provided on the firstintermediate layer 30 a (an MgO layer), for example. On the firstmagnetic layer 10 a, an MgO layer with a thickness of 1.5 nm is providedas the functional layer 15 a. Thereby, the structure of CoFeB layer ismade amorphous (including a microcrystalline structure). In this case,the coercive force is 4 Oe or less, and the value of the GF is not lessthan 3,000 and not more than 4,000.

FIG. 5A to FIG. 5I and FIG. 6A to FIG. 6I are graphs illustratingcharacteristics of inertial sensors.

FIG. 5A to FIG. 5I show characteristics of a first sample S01. FIG. 6Ato FIG. 6I are graphs showing characteristics of a second sample S02. Inthe first sample S01, the MgO layer mentioned above is used as thefunctional layer 15 a. In the second sample S02, a Ta layer is used asthe functional layer 15 a.

FIG. 5A to FIG. 5I show the measurement results of the magnetic fielddependence of the electric resistance when the strain ε is 0.8×10⁻³,0.6×10⁻³, 0.4×10⁻³, 0.2×10⁻³, 0.0×10⁻³, −0.2×10⁻³, −0.4×10⁻³, −0.6×10⁻³,and −0.8×10⁻³, respectively. FIG. 6A to FIG. 6I show the measurementresults of the magnetic field dependence of the electric resistance whenthe strain ε is 0.8×10⁻³, 0.6×10⁻³, 0.4×10⁻³, 0.2×10⁻³, 0.0×10⁻³,−0.2×10⁻³, −0.4×10⁻³, −0.6×10⁻³, and −0.8×10⁻³, respectively.

As shown in the drawings, the characteristics change greatly with thematerial of the functional layer 15 a.

FIG. 7A and FIG. 7B are graphs illustrating characteristics of inertialsensors.

FIG. 7A corresponds to the first sample S01, and FIG. 7B corresponds tothe second sample S02. The drawings show the change in electricresistance R when the external magnetic field H is fixed and the strainε is changed continuously in a range between −0.8×10⁻³ and 0.8×10⁻³. Thehorizontal axis of the drawings is the strain E, and the vertical axisis the electric resistance R. The change in strain ε includes both thechange from −0.8×10⁻³ toward 0.8×10⁻³ and the change from 0.8×10⁻³toward −0.8×10⁻³. The results show strain sensor characteristics. Thegauge factor GF is calculated from the drawings.

From FIG. 7A, the gauge factor in the first sample S01 is calculated tobe 4027. From FIG. 7B, the gauge factor in the second sample S02 iscalculated to be 859.

Thus, a large gauge factor can be obtained by using the functional layer15 a of MgO to make the first magnetic layer 10 a an amorphousstructure.

It is presumed that the functional layer 15 a of MgO suppresses thediffusion of B from the first magnetic layer 10 a. The functional layer15 a functions as a diffusion barrier layer, for example. An MgO layerwith a low sheet resistance is provided as the functional layer 15 a,for example. A layer having a sheet resistance of approximately not morethan 5 times the sheet resistance of the MgO layer used as the firstintermediate layer 30 a is used as the functional layer 15 a, forexample. The design is made so that the sheet resistance RA of the wholestacked film is not increased substantially when the functional layer 15a is provided

Examples of the difference in the crystal state of the first magneticlayer 10 a depending on the presence or absence of the functional layer15 a will now be described.

FIG. 8A to FIG. 8D are microscope images illustrating characteristics ofan inertial sensor.

FIG. 9A to FIG. 9D are microscope images illustrating characteristics ofan inertial sensor.

FIG. 8A to FIG. 8D correspond to the first sample S01, and FIG. 9A toFIG. 9D correspond to the second sample S02.

FIG. 8A is a cross-sectional transmission electron microscope(cross-sectional TEM) photographic image of the inertial sensor of thefirst sample S01. FIG. 8B to FIG. 8D are crystal lattice diffractionimages obtained by nanodiffraction of an electron beam of points P1 toP3 of FIG. 8A, respectively. FIG. 9A is a photograph of the stackedstructure of the second sample S02. FIG. 9B to FIG. 9D are crystallattice diffraction images obtained by nanodiffraction of an electronbeam of points P4 to P6 of FIG. 9A, respectively.

As shown in FIG. 8A, in the first sample S01, the first intermediatelayer 30 a is provided on the second magnetic layer 20 a, and the firstmagnetic layer 10 a is provided on the first intermediate layer 30 a.The functional layer 15 a is provided on the first magnetic layer 10 a.A cap layer 45 is provided on the functional layer 15 a. On the otherhand, as shown in FIG. 9A, the functional layer 15 a is not provided inthe second sample S02.

As can be seen from FIG. 8A, the second magnetic layer 20 a iscrystalline. Also the first intermediate layer 30 a is crystalline. Onthe other hand, in the most part of the first magnetic layer 10 a, aregular arrangement of atoms is not observed. That is, the firstmagnetic layer 10 is amorphous.

As shown in FIG. 8B, diffraction spots are observed in the diffractionimage of point P1 corresponding to the second magnetic layer 20 a. Thediffraction spots are due to the fact that the second magnetic layer 20a has a crystal structure.

As shown in FIG. 8C, diffraction spots are observed in the diffractionimage of point P2 corresponding to the first intermediate layer 30 a.The diffraction spots are due to the fact that the intermediate layer 30has a crystal structure.

On the other hand, as shown in FIG. 8D, distinct diffraction spots arenot observed in the diffraction image of point P3 corresponding to thefirst magnetic layer 10 a. In the diffraction image, a ring-likediffraction image reflecting an amorphous structure is observed. It isfound that the first magnetic layer 10 a of the first sample S01includes an amorphous portion.

As can be seen from FIG. 9A, the second magnetic layer 20 a and thefirst intermediate layer 30 a are a crystal. Also the first magneticlayer 10 a is crystalline.

As shown in FIG. 9B, diffraction spots due to a crystal structure arefound in the diffraction image of the second magnetic layer 20 a.

As shown in FIG. 9C, diffraction spots due to a crystal structure arefound in the diffraction image of the first intermediate layer 30 a.

As shown in FIG. 9D, diffraction spots due to a crystal structure arefound also in the diffraction image of the first magnetic layer 10 a.The result shows that the most part of the first magnetic layer 10 a ofthe second sample S02 has a crystal structure.

A high gauge factor is obtained by using the first magnetic layer 10 aincluding an amorphous portion, like the first sample S01 mentionedabove.

FIG. 10 is a graph illustrating characteristics of an inertial sensor.

In this example, an FeB material of an amorphous structure (including amicrocrystalline structure) is used for both the first magnetic layer 10a and the second magnetic layer 20 a. From FIG. 10, the calculated gaugefactor is 5290. Thus, a high gauge factor is obtained by using amagnetic layer of an amorphous structure.

When the first intermediate layer 30 a is a metal, the GMR effect isexhibited, for example. When the first intermediate layer 30 a is aninsulator, the TMR effect is exhibited. In the sensing element unit 50,the CPP (current perpendicular to plane)-GMR effect in which a currentis passed along the stacking direction of the resistance change unit isused, for example.

A CCP (current-confined-path) spacer layer may be used as the firstintermediate layer 30 a. In the CCP spacer layer, a metal current pathwith a width (for example, diameter) of 1 nm or more, approximately 5nm, is formed in plural in a part of an insulating layer so as topenetrate in the film thickness direction. The CPP-GMR effect is usedalso in the CCP spacer layer.

Thus, in the embodiment, the inverse magnetostriction phenomenon in thesensing element unit 50 is used. Thereby, high-sensitivity sensingbecomes possible. When the inverse magnetostriction effect is used, themagnetization direction of at least one of the first magnetic layer 10 aand the second magnetic layer 20 a changes with the strain applied fromthe outside, for example. The relative angle between the magnetizationsof the two magnetic layers changes with the strain generated byacceleration (the presence or absence, the level thereof, etc.). Sincethe electric resistance changes with the strain generated byacceleration, the sensing element unit 50 functions as an inertialsensor.

FIG. 11A and FIG. 11B are schematic perspective views illustrating partof the inertial sensor according to the first embodiment.

As shown in FIG. 11A, the sensing element unit 50 includes the firstelectrode 51 a and the second electrode 52 a, for example. The firstresistance change unit 50 sa is provided between the first electrode 51a and the second electrode 52 a. In this example, in the firstresistance change unit 50 sa, a buffer layer 41, an antiferromagneticlayer 42, a magnetic layer 43, a Ru layer 44, the second magnetic layer20 a, the first intermediate layer 30 a, the first magnetic layer 10 a,and the cap layer 45 are provided in this order from the first electrode51 a side toward the second electrode 52 a side.

The buffer layer 41 may serve also as a seed layer. The thickness of thebuffer layer 41 is not less than 1 nm and not more than 10 nm, forexample. As the buffer layer 41, an amorphous layer including Ta, Ti, orthe line is used, for example. As the buffer layer 41, a layer of Ru,NiFe, or the like serving as a seed layer for the promotion of crystalorientation is used. A stacked film of these films may be used as thebuffer layer 41. The thickness of the antiferromagnetic layer 42 is notless than 5 nm and not more than 10 nm, for example. The thickness ofthe magnetic layer 43 is not less than 2 nm and not more than 6 nm, forexample. In this example, the thickness of the second magnetic layer 20a is not less than 2 nm and not more than 5 nm, for example. Thethickness of the first intermediate layer 30 a is not less than 1 nm andnot more than 3 nm, for example. The thickness of the first magneticlayer 10 a is not less than 2 nm and not more than 5 nm, for example.The thickness of the cap layer 45 is not less than 1 nm and not morethan 5 nm, for example.

As the second magnetic layer 20 a, also a magnetic stacked film may beused, for example. On the other hand, the first magnetic layer 10 a mayinclude a magnetic stacked film 10 p for increasing the MR ratio and ahigh magnetostriction magnetic film 10 q. The high magnetostrictionmagnetic film 10 q is provided between the magnetic stacked film 10 pand the cap layer 45. The magnetic stacked film 10 p increases the MRratio, for example. The thickness of the magnetic stacked film 10 p isnot less than 1 nm and not more than 3 nm, for example. For the magneticstacked film 10 p, an alloy including CoFe, CoFe, and the like are used,for example. The thickness of the high magnetostriction magnetic film 10q is not less than 1 nm and not more than 5 nm, for example.

For the first electrode 51 a and the second electrode 52 a, Au, Cu, Ta,Al, and the like, which are nonmagnetic materials, may be used, forexample. As the first electrode 51 a and the second electrode 52 a, asoft magnetic material may be used; thereby, magnetic noise from theoutside that influences the resistance change unit can be reduced. Asthe soft magnetic material, permalloy (NiFe alloy) and silicon steel(FeSi alloy) may be used, for example. The sensing element unit 50 iscovered with an insulator such as an aluminum oxide (for example, Al₂O₃)and a silicon oxide (for example, SiO₂). Thereby, leakage current issuppressed.

The magnetization direction of at least one of the first magnetic layer10 a and the second magnetic layer 20 a changes in accordance with thestress. The absolute value of the magnetostriction constant of at leastone magnetic layer (the magnetic layer of which the magnetizationdirection changes in accordance with the stress) is preferably set to10⁻⁵ or more, for example. Thereby, it becomes easier for themagnetization direction to change in accordance with the strain appliedfrom the outside, due to the inverse magnetostriction effect. For atleast one of the first magnetic layer 10 a and the second magnetic layer20 a, a metal such as Fe, Co, and Ni, an alloy including them, or thelike is used, for example. The magnetostriction constant is set large bythe element used, additive elements, etc. The absolute value of themagnetostriction constant is preferably large. In view of materials thatcan be used as practical devices, absolute values of themagnetostriction constant of approximately 10⁻² or less are practical.

As at least one of the first magnetic layer 10 a and the second magneticlayer 20 a, a magnetic layer of an amorphous structure including Fe ispreferably used as a material by which a high strain sensitivity (gaugefactor GF) is obtained, as described above, for example. In such amaterial, a GF of approximately 5,000 is obtained. It is presumed that aGF of approximately 10,000 can be obtained by optimization.

As the first intermediate layer 30 a, an oxide such as MgO is used, forexample. A magnetic layer on an MgO layer generally has a plusmagnetostriction constant. In the case where the first magnetic layer 10a is formed on the first intermediate layer 30 a, a stacked film ofCoFeB/CoFe/NiFe is used as the first magnetic layer 10 a, for example.When the uppermost NiFe layer is made Ni-rich, the absolute value of themagnetostriction constant of the NiFe layer is large in the minus. Tosuppress the cancellation of the plus magnetostriction on an oxidelayer, the uppermost NiFe layer is not made Ni-rich as compared to thepermalloy of Ni₈₁Fe₁₉ commonly used. Specifically, the ratio of Ni inthe uppermost NiFe layer is preferably set less than 80 atomic percent(atomic %). In the case where a magnetization free layer is used as thefirst magnetic layer 10 a, the thickness of the first magnetic layer 10a is preferably not less than 1 nm and not more than 20 nm, for example.

In the case where the first magnetic layer 10 a is a magnetization freelayer, the second magnetic layer 20 a may be either a magnetizationfixed layer or a magnetization free layer. In the case where the secondmagnetic layer 20 a is a magnetization fixed layer, the magnetizationdirection of the second magnetic layer 20 a does not changesubstantially even when a strain is applied from the outside. Theelectric resistance changes with the relative angle between themagnetizations of the first magnetic layer 10 a and the second magneticlayer 20 a. The presence or absence of strain is sensed by thedifference in electric resistance. Thereby, the acceleration is sensed.

In the case where both the first magnetic layer 10 a and the secondmagnetic layer 20 a are a magnetization free layer, the magnetostrictionconstant of the first magnetic layer 10 a is differentiated from themagnetostriction constant of the second magnetic layer 20 a, forexample.

In the case where the second magnetic layer 20 a is either amagnetization fixed layer or a magnetization free layer, the thicknessof the second magnetic layer 20 a is preferably not less than 1 nm andnot more than 20 nm, for example.

In the case where the second magnetic layer 20 a is a magnetizationfixed layer, a synthetic AF structure using a stacked structure of anantimagnetic layer/a magnetic layer/a Ru layer/a magnetic layer and thelike may be used as the second magnetic layer 20 a, for example. For theantimagnetic layer, IrMn and the like are used, for example. A hard biaslayer may be provided.

A very small size is sufficient for the area necessary for the sensingelement unit 50. In terms of the size of a square, the sensing elementunit 50 needs only to have a size of 10 nm×10 nm to 20 nm×20 nm or more(one side×one side) as the minimum size, for example.

On the other hand, such a small element size increases the degree ofdifficulty in measures against antimagnetic fields because the elementis operated as a sensor. When the element size is sufficiently smallerthan the MEMS structure body, since the area to arrange elements issufficient, in practical terms the element size is preferably increasedso as to facilitate antimagnetic field measures and noise measures, forexample. Examples of the element size are described below.

The area of the sensing element unit 50 is set sufficiently smaller thanthe area of the connection portion 74 that bends due to pressure. Thearea of the sensing element unit 50 is not more than ⅕ of the area ofthe planar shape of the weight portion 72, for example. The size of theweight portion 72 is approximately not less than 60 μm and not more than600 μm, for example. When the diameter of the planar shape of the weightportion 72 is approximately 60 μm, the length of one side of the sensingelement unit 50 is 12 μm or less, for example. When the diameter of theplanar shape of the weight portion 72 is 600 μm, the length of one sideof the sensing element unit 50 is 120 μm or less, for example.

As compared to the value of this upper limit, the size of the length ofone side of not less than 10 nm and not more than 20 nm mentioned aboveis extremely small. Hence, in view of also the processing accuracy ofthe element etc., there is no need to make the sensing element unit 50excessively small. Thus, the size of one side of the sensing elementunit 50 is preferably set approximately not less than 0.5 μm and notmore than 60 μm in practical terms, for example. If the element size isextremely small, the magnitude of the antimagnetic field generated inthe sensing element unit 50 is increased; thus, the problem arises thatthe bias control of the sensing element unit 50 is difficult, or thelike. When the element size is large, the problem of antimagnetic fieldsis not presented, and handling is thus easy in the engineeringviewpoint. From this viewpoint, not less than 0.5 μm and not more than60 μm are preferable sizes.

The length along the X-axis direction of the sensing element unit 50 ispreferably not less than 0.5 μm and not more than 60 μm, for example.The length along the X-axis direction of the sensing element unit 50 ismore preferably not less than 1 μm and not more than 20 μm.

The length along the Y-axis direction (the direction perpendicular tothe X-axis direction and parallel to the X-Y plane) of the sensingelement unit 50 is preferably not less than 0.5 μm and not more than 60μm, for example. The length along the Y-axis direction of the sensingelement unit 50 is more preferably in a range of not less than 1 μm andnot more than 20 μm.

The thickness (length) along the Z-axis direction (the directionperpendicular to the X-Y plane) of the sensing element unit 50 is notless than 20 nm and not more than 100 nm, for example. The thickness isdetermined by the film thickness of the stacked films, for example.

The length along the X-axis direction of the sensing element unit 50 maybe equal to or different from the length along the Y-axis direction ofthe sensing element unit 50. When the length along the X-axis directionof the sensing element unit 50 is different from the length along theY-axis direction of the sensing element unit 50, shape magneticanisotropy occurs. Thereby, effects similar to the effects obtained by ahard bias layer can be obtained.

The direction of the current passed through the sensing element unit 50may be the direction from the first magnetic layer 10 a toward thesecond magnetic layer 20 a, or may be the direction from the secondmagnetic layer 20 a toward the first magnetic layer 10 a. The inertialsensor 310 according to the embodiment can provide an inertial sensorthat senses acceleration, displacement, etc. with high sensitivity.

There is a piezoresistance inertial sensor using Si, for example. Inthis case, the strain sensitivity (gauge factor GF) is determined by thematerial used, and the gauge factor GF is approximately 130, forexample. In the case of the piezoresistance inertial sensor using Si, anelement area of approximately 100 μm in terms of one side is needed. Thegauge factor GF per unit area is 130/100 μm², and is approximately 10¹⁰,for example.

On the other hand, in the inertial sensor according to the embodiment, aspin strain sensor is used as the sensing element unit 50. As describedabove, a gauge factor of approximately 4000 to 5000 is obtained. In theembodiment, higher gauge factors GF are obtained by using magneticlayers. Even a gauge factor GF of approximately 10,000 is obtained, forexample. The element area necessary to achieve this gauge factor GF isapproximately 100 nm in terms of one side, as described above.Accordingly, the gauge factor GF per unit area is approximately 10¹⁷,for example. Thus, in the embodiment, improvements in sensitivity perunit area of approximately seven digits are possible as compared to thecase of the inertial sensor of a MEMS structure using Si, for example.In other words, sensitivities substantially equal to existing ones canbe achieved even by small devices. Properties higher than conventionalones are obtained with sizes substantially equal to conventional ones.Properties such as high sensitivities, wide frequency ranges, and widedynamic ranges are obtained, for example. The embodiment can provide aninertial sensor that has been difficult for conventional technology toprovide.

As shown in FIG. 11B, the inertial sensor 50 may include bias layers 55a and 55 b (hard bias layers). The bias layers 55 a and 55 b areprovided to oppose a strain resistance change unit 50 s.

In this example, the second magnetic layer 20 is a magnetization fixedlayer. The bias layers 55 a and 55 b are juxtaposed to the secondmagnetic layer 20. The strain resistance change unit 50 s is disposedbetween the bias layers 55 a and 55 b. An insulating layer 54 a isprovided between the bias layer 55 a and the strain resistance changeunit 50 s. An insulating layer 54 b is provided between the bias layer55 b and the strain resistance change unit 50 s.

The bias layers 55 a and 55 b apply a bias magnetic field to the firstmagnetic layer 10. Thereby, the magnetization direction of the firstmagnetic layer 10 can be biased to an appropriate position, and can bemade into a single magnetic domain

The size (in this example, the length along the Y-axis direction) ofeach of the bias layers 55 a and 55 b is not less than 100 nm and notmore than 10 μm, for example.

The size (in this example, the length along the Y-axis direction) ofeach of the insulating layers 54 a and 54 b is not less than 1 nm andnot more than 5 nm, for example.

Second Embodiment

FIG. 12 is a schematic perspective view illustrating an inertial sensoraccording to a second embodiment.

As shown in FIG. 12, in an inertial sensor 320, a second sensing elementunit 50 b is further provided in addition to the first sensing elementunit 50 a. That is, the connection portion 74 further includes a secondportion 74 b in addition to the first portion 74 a. The second sensingelement unit 50 b is provided on the second portion 74 b, for example.The second sensing element unit 50 b is fixed to the second portion 74b.

In this example, a third sensing element unit 50 c and a fourth sensingelement unit 50 d are further provided. That is, the connection portion74 further includes a third portion 74 c and a fourth portion 74 d. Thethird sensing element unit 50 c is provided on the third portion 74 c.The third sensing element unit 50 c is fixed to the third portion 74 c.The fourth sensing element unit 50 d is provided on the fourth portion74 d. The fourth sensing element unit 50 d is fixed to the fourthportion 74 d. The first to fourth sensing element units 50 a to 50 d areincluded in the sensing element unit 50. As described later, the numberof sensing element units 50 may be 5 or more.

In this example, a first interconnection 57 and a second interconnection58 are provided on the base portion 71. In this example, at least a partof the first interconnection 57 and the second interconnection 58 isprovided on the upper surface of the base portion 71. The firstinterconnection 57 and the second interconnection 58 are electricallyconnected to each of the sensing element units 50.

In this example, the first to fourth portions 74 a to 74 d are apartfrom one another. That is, the connection portion 74 includes aplurality of portions apart from one another. In this example, theconnection portion 74 holds a plurality of portions apart from oneanother of the weight portion 72.

As described later, the embodiment is not limited thereto, and the firstto fourth portions 74 a to 74 d may be continuous. That is, theconnection portion 74 may be continuously connected to the outer edge ofthe weight portion 72.

As shown in FIG. 12, the first to fourth sensing element units 50 a to50 d are provided substantially in one plane. A plane parallel to thedirection from the base portion 71 toward the weight portion 72 and tothe direction from the first portion 74 a toward the second portion 74 bis formed, for example. In this example, the plane is the X-Y plane. Inthis example, the first to fourth sensing element units 50 a to 50 d areprovided in the X-Y plane.

When projected onto the X-Y plane, the line connecting the centroid 72 cof the weight portion 72 and the first sensing element unit 50 a crossesthe line connecting the centroid 72 c of the weight portion 72 and thesecond sensing element unit 50 b, for example. In this example, whenprojected onto the X-Y plane, the line connecting the first sensingelement unit 50 a and the third sensing element unit 50 c passes throughthe centroid 72 c of the weight portion 72. In this example, whenprojected onto the X-Y plane, the line connecting the second sensingelement unit 50 b and the fourth sensing element unit 50 d passesthrough the centroid 72 c of the weight portion 72.

The first to fourth sensing element units 50 a to 50 d are aligned alongthe outer edge 72 c of the weight portion 72.

FIG. 13A to FIG. 13C are schematic cross-sectional views illustratingthe inertial sensor according to the second embodiment.

As shown in FIG. 13A, the second sensing element unit 50 b includes athird magnetic layer 10 b, a fourth magnetic layer 20 b, and a secondintermediate layer 30 b. The second intermediate layer 30 b is providedbetween the third magnetic layer 10 b and the fourth magnetic layer 20b, and is nonmagnetic. The third magnetic layer 10 b, the fourthmagnetic layer 20 b, and the second intermediate layer 30 b are includedin a second resistance change unit 50 sb. In this example, a thirdelectrode 51 b and a fourth electrode 52 b are further provided. Thesecond resistance change unit 50 sb is disposed between the thirdelectrode 51 b and the fourth electrode 52 b. In this example, the thirdmagnetic layer 10 b is disposed between the third electrode 51 b and thefourth electrode 52 b, and the fourth magnetic layer 20 b is disposedbetween the third magnetic layer 10 b and the third electrode 51 b.

As shown in FIG. 13B, the third sensing element unit 50 c includes afifth magnetic layer 10 c, a sixth magnetic layer 20 c, and a thirdintermediate layer 30 c. The third intermediate layer 30 c is providedbetween the fifth magnetic layer 10 c and the sixth magnetic layer 20 c,and is nonmagnetic. The fifth magnetic layer 10 c, the sixth magneticlayer 20 c, and the third intermediate layer 30 c are included in athird resistance change unit 50 sc. In this example, a fifth electrode51 c and a sixth electrode 52 c are further provided. The thirdresistance change unit 50 sc is disposed between the fifth electrode 51c and the sixth electrode 52 c.

As shown in FIG. 13C, the fourth sensing element unit 50 d includes aseventh magnetic layer 10 d, an eighth magnetic layer 20 d, and a fourthintermediate layer 30 d. The fourth intermediate layer 30 d is providedbetween the seventh magnetic layer 10 d and the eighth magnetic layer 20d, and is nonmagnetic. The seventh magnetic layer 10 d, the eighthmagnetic layer 20 d, and the fourth intermediate layer 30 d are includedin a fourth resistance change unit 50 sd. In this example, a seventhelectrode 51 d and an eighth electrode 52 d are further provided. Thefourth resistance change unit 50 sd is disposed between the seventhelectrode 51 d and the eighth electrode 52 d.

The third magnetic layer 10 b, the fifth magnetic layer 10 c, and theseventh magnetic layer 10 d are a magnetization free layer, for example.The material and configuration described in regard to the first magneticlayer 10 a are used for these magnetic layers.

The fourth magnetic layer 20 b, the sixth magnetic layer 20 c, and theeighth magnetic layer 20 d are a reference layer, for example. Thesemagnetic layers are a magnetization free layer or a magnetization fixedlayer, for example. The material and configuration described in regardto the second magnetic layer 20 a are used for these magnetic layers.

FIG. 14A and FIG. 14B are schematic plan views illustrating the inertialsensor according to the second embodiment.

FIG. 14A and FIG. 14B correspond to the first state ST1 and the secondstate ST2, respectively.

As shown in FIG. 14A, one plane (for example, the X-Y plane) includesthe direction from the base portion 71 toward the weight portion 72 andthe direction from the first portion 74 a toward the second portion 74b. The direction connecting the position of the centroid 72 c of theweight portion 72 in the plane (the X-Y plane) and the position of thefirst portion 74 a in the plane is defined as a first direction LN1, forexample. On the other hand, the direction connecting the position of thecentroid 72 c of the weight portion 72 in the plane and the position ofthe second portion 74 b in the plane is defined as a second directionLN2. The first direction LN1 crosses the second direction LN2. In thisexample, the angle between the first direction LN1 and the seconddirection LN2 is substantially 90 degrees. This angle is larger than 0degrees and smaller than 180 degrees, for example.

When projected onto the X-Y plane, a plurality of sensing element units50 are arranged along the circumference of a circle with center at thecentroid 72 c of the weight portion 72.

In the first state ST1, in the first sensing element unit 50 a, thedirection of the magnetization of the first magnetic layer 10 a (a firstlayer magnetization direction 10 am) runs along the direction of themagnetization of the second magnetic layer 20 a (a second layermagnetization direction 20 am), for example. In this example, the firstlayer magnetization direction 10 am is antiparallel to the second layermagnetization direction 20 am.

In the first state ST1, in the second sensing element unit 50 b, thedirection of the magnetization of the third magnetic layer 10 b (a thirdlayer magnetization direction 10 bm) runs along the direction of themagnetization of the fourth magnetic layer 20 b (a fourth layermagnetization direction 20 bm), for example. In this example, the thirdlayer magnetization direction 10 bm is antiparallel to the fourth layermagnetization direction 20 bm.

In the first state ST1, in the third sensing element unit 50 c, thedirection of the magnetization of the fifth magnetic layer 10 c (a fifthlayer magnetization direction 10 cm) runs along the direction of themagnetization of the sixth magnetic layer 20 c (a sixth layermagnetization direction 20 cm), for example. In this example, the fifthlayer magnetization direction 10 cm is antiparallel to the sixth layermagnetization direction 20 cm.

In the first state ST1, in the fourth sensing element unit 50 d, thedirection of the magnetization of the seventh magnetic layer 10 d (aseventh layer magnetization direction 10 dm) runs along the direction ofthe magnetization of the eighth magnetic layer 20 d (an eighth layermagnetization direction 20 dm), for example. In this example, theseventh layer magnetization direction 10 dm is antiparallel to theeighth layer magnetization direction 20 dm.

For easier description, it is assumed that the reference layer 20 (thesecond magnetic layer 20 a, the fourth magnetic layer 20 b, the sixthmagnetic layer 20 c, the eighth magnetic layer 20 d, and the like) is amagnetization fixed layer.

The direction of the magnetization of the second magnetic layer 20 a(the second layer magnetization direction 20 am) crosses the directionof the magnetization of the fourth magnetic layer 20 b (the fourth layermagnetization direction 20 bm). The angle between the second layermagnetization direction 20 am and the fourth layer magnetizationdirection 20 bm is 90 degrees, for example.

In this example, the direction of the magnetization of the sixthmagnetic layer 20 c (the sixth layer magnetization direction 20 cm) isparallel to the direction of the magnetization of the second magneticlayer 20 a (the second layer magnetization direction 20 am). Thedirection of the magnetization of the eighth magnetic layer 20 d (theeighth layer magnetization direction 20 dm) is parallel to the directionof the magnetization of the fourth magnetic layer 20 b (the fourth layermagnetization direction 20 bm).

As shown in FIG. 14B, on entering the second state ST2, the direction ofthe magnetization of the magnetization free layer 10 (the first magneticlayer 10 a, the third magnetic layer 10 b, the fifth magnetic layer 10c, the seventh magnetic layer 10 d, and the like) changes from that inthe first state ST1.

As shown in FIG. 14A, in the first magnetic layer 10 a, when therelative position of the weight portion 72 with respect to the baseportion 71 is in the first state ST1, the magnetization of the firstmagnetic layer 10 a (the first layer magnetization direction 10 am) isin a first magnetization direction, for example. In this example, thefirst magnetization direction in the first state ST1 (the first layermagnetization direction 10 am) runs along the Y-axis direction. As shownin FIG. 14B, when the relative position of the weight portion 72 withrespect to the base portion 71 is in the second state ST2 different fromthe first state ST1, the magnetization of the first magnetic layer 10 a(the first layer magnetization direction 10 am) is in a directiondifferent from the first magnetization direction in the first state ST1.In this example, the magnetization of the first magnetic layer 10 a (thefirst layer magnetization direction 10 am) in the second state ST2 isinclined with respect to the Y-axis direction. Thereby, in the firstsensing element unit 50 a, the electric resistance changes between thefirst state ST1 and the second state ST2.

Similarly, as shown in FIG. 14A, in the second sensing element unit 50b, when the relative position of the weight portion 72 with respect tothe base portion 71 is in the first state ST1, the magnetization of thethird magnetic layer 10 b (the third layer magnetization direction 10bm) is in a third magnetization direction. In this example, the thirdmagnetization direction in the first state ST1 (the third layermagnetization direction 10 bm) runs along the X-axis direction. As shownin FIG. 14B, when the relative position of the weight portion 72 withrespect to the base portion 71 is in the second state ST2, themagnetization of the third magnetic layer 10 b (the third layermagnetization direction 10 bm) is in a direction different from thethird magnetization direction in the first state ST1. In this example,the magnetization of the third magnetic layer 10 b (the third layermagnetization direction 10 bm) in the second state ST2 is inclined withrespect to the X-axis direction. Thereby, in the second sensing elementunit 50 b, the electric resistance changes between the first state ST1and the second state ST2.

In the inertial sensor 320, with the centroid 72 c of the weight portion72 as a reference, a plurality of sensing element units 50 are arrangedin different directions. Thereby, accelerations in different directionscan be sensed. With the centroid 72 c of the weight portion 72 as areference, the direction of the magnetization of the reference layer(the second magnetic layer 20 a) in the first sensing element unit 50 adisposed in the X-axis direction and the direction of the magnetizationof the reference layer (the fourth magnetic layer 20 b) in the secondsensing element unit 50 b disposed in the Y-axis direction cross eachother; thereby, accelerations along the X-axis direction andaccelerations along the Y-axis direction can be sensed, for example.Also accelerations along the Z-axis direction can be sensed. Theinertial sensor 320 can sense accelerations in arbitrary directions ofthree axes.

In the case where the reference layer 20 is a magnetization fixed layer,the direction of the magnetization of each of the plurality of referencelayers 20 may be set in accordance with the positioning of each of theplurality of reference layers 20. As shown in FIG. 14A, in this example,the angle between the first direction LN1 and the second direction LN2is 90 degrees. At this time, the angle between the direction of themagnetization of the second magnetic layer 20 a and the direction of themagnetization of the fourth magnetic layer 20 b is 90 degrees. It isassumed that, when the angle between the first direction LN1 and thesecond direction LN2 is not less than 70 degrees and not more than 110degrees, the angle between the direction of the magnetization of thesecond magnetic layer 20 a and the direction of the magnetization of thefourth magnetic layer 20 b is not less than 70 degrees and not more than110 degrees, for example. The properties in the sensing element units 50are substantially symmetric, and sensing sensitivity can be enhanced.

Although this example is described for the case where the referencelayer 20 is a magnetization fixed layer, the reference layer 20 may be amagnetization free layer. In this case, when the relative position ofthe weight portion 72 with respect to the base portion 71 is in thefirst state ST1, the magnetization of the first magnetic layer 10 a isin a first magnetization direction, and the magnetization of the secondmagnetic layer 20 a is in a second magnetization direction, for example.When the relative position of the weight portion 72 with respect to thebase portion 71 is in the second state ST2 different from the firststate ST1, the magnetization of the first magnetic layer 10 a is in adirection different from the first magnetization direction, and themagnetization of the second magnetic layer 20 a is in a directiondifferent from the second magnetization direction. Thereby, in the firstsensing element unit 50 a, the electric resistance changes between thefirst state ST1 and the second state ST2.

On the other hand, when the relative position of the weight portion 72with respect to the base portion 71 is in the first state ST1, themagnetization of the third magnetic layer 10 b is in a thirdmagnetization direction, and the magnetization of the fourth magneticlayer 20 b is in a fourth magnetization direction. When the relativeposition of the weight portion 72 with respect to the base portion 71 isin the second state ST2, the magnetization of the third magnetic layer10 b is in a direction different from the third magnetization direction,and the magnetization of the fourth magnetic layer 20 b is in adirection different from the fourth magnetization direction. Thereby, inthe second sensing element unit 50 b, the electric resistance changesbetween the first state ST1 and the second state ST2.

Thus, each of the sensing element units 50 is provided in each of theplurality of positions of the connection portion 74 (for example, thefirst portion 74 a and the second portion 74 b). In the case where amagnetization fixed layer is used as the reference layer 20, thedirection of the magnetization of the second magnetic layer 20 a in thefirst sensing element unit 50 a and the direction of the magnetizationof the fourth magnetic layer 20 b in the second sensing element unit 50b may be differentiated from each other; thereby, accelerations in thedirections of three axes are sensed. Alternatively, by using amagnetization free layer as the reference layer 20, accelerations in thedirections of three axes are sensed.

FIG. 15A and FIG. 15B are schematic plan views illustrating otherinertial sensors according to the second embodiment.

As shown in FIG. 15A, in an inertial sensor 320 a according to theembodiment, a plurality of sensing element units 50 are provided. Inthis example, the number of sensing element units 50 is eight. In theembodiment, the number of sensing element units 50 is arbitrary.

In this example, the magnetization 20 m of the reference layer 20 ofeach of the sensing element units 50 is orthogonal to the lineconnecting each sensing element unit 50 and the centroid 72 c of theweight portion 72. The magnetization 10 m of the magnetization freelayer 10 of each of the sensing element units 50 is substantiallyparallel (in this example, antiparallel) to the magnetization 20 m ofthe reference layer 20 of each sensing element unit 50.

In the embodiment, the angle with the line connecting the magnetization20 m of the reference layer 20 of each of the sensing element units 50and the centroid 72 c of the weight portion 72 may be altered from 90degrees. The angle between the magnetization 10 m of the magnetizationfree layer 10 of each of the sensing element units 50 and themagnetization 20 m of the reference layer 20 of each sensing elementunit 50 may be altered from 0 degrees or 180 degrees.

As shown in FIG. 15B, in an inertial sensor 320 b according to theembodiment, the connection portion 74 is continuous, and the firstportion 74 a is continuous with the second portion 74 b, for example.

In the embodiment, when the first portion 74 a and the second portion 74b are separated, the degree of deformation of the connection portion 74with respect to the applied acceleration is increased, and sensingsensitivity is enhanced. On the other hand, when the connection portion74 is continuous, the mechanical strength of the connection portion 74is enhanced. The connection portion 74 is designed in accordance withthe thickness of the connection portion 74, the necessary sensingsensitivity, and the viewpoint of reliability.

When the connection portion 74 is thin, high sensing sensitivity isobtained, for example. The X-Y plane is a plane parallel to thedirection from the base portion 71 toward the weight portion 72 and tothe direction from the first portion 74 a toward the second portion 74b, for example. The direction perpendicular to the X-Y plane (forexample, the Z-axis direction) is defined as a third direction. Thelength (thickness) of the first portion 74 a along the third directionis shorter (thinner) than the length (thickness) of the weight portion72 along the third direction (the Z-axis direction). The length(thickness) of the second portion 74 b along the third direction (theZ-axis direction) is shorter (thinner) than the length (thickness) ofthe weight portion 72 along the third direction (the Z-axis direction).

The width of the first portion 74 a and the width of the second portion74 b are narrower than the width of the weight portion 72. The firstportion 74 a and the second portion 74 b are separated from each other,for example. At this time, the direction parallel to the X-Y plane andperpendicular to the first direction LN1 is defined as a fourthdirection. The length (width) of the first portion 74 a along the fourthdirection is shorter than the length (width) of the weight portion 72along the fourth direction. On the other hand, the direction parallel tothe X-Y plane and perpendicular to the second direction LN2 is definedas a fifth direction. The length (width) of the second portion 74 balong the fifth direction is shorter than the length (width) of theweight portion 72 along the fifth direction. Thereby, it becomes easierto obtain high sensing sensitivity.

Third Embodiment

FIG. 16A and FIG. 16B are schematic perspective views illustrating aninertial sensor according to a third embodiment.

FIG. 16A illustrates the first sensing element unit 50 a in an inertialsensor 330 according to the embodiment. FIG. 16B illustrates the secondsensing element unit 50 b in the inertial sensor 330. In the drawings,the base portion 71 and the weight portion 72 are omitted. The baseportion 71 and the weight portion 72 in the inertial sensor 330 aresimilar to those described in regard to the first and secondembodiments, for example.

As shown in FIG. 16A, the first magnetic layer 10 a extends along afirst extending direction Dea1. The first extending direction Dea1crosses a first stacking direction Dza1 from the first magnetic layer 10a toward the second magnetic layer 20 a (for example, the Z-axisdirection). In this example, the first extending direction Dea1 isperpendicular to the first stacking direction Dza1. The first magneticlayer 10 a has a length along the first extending direction Dea1 (afirst major axis length Lea1). The first magnetic layer 10 a has alength in a direction (direction Dfa1) crossing the first stackingdirection Dza1 and crossing the first extending direction Dea1 (a firstminor axis length Lfa1). The first major axis length Lea1 of the firstmagnetic layer 10 a is longer than the first minor axis length Lfa1 ofthe first magnetic layer 10 a.

The second magnetic layer 20 a extends along a second extendingdirection Dea2. The second extending direction Dea2 crosses the firststacking direction Dza1 from the first magnetic layer 10 a toward thesecond magnetic layer 20 a (for example, the Z-axis direction). In thisexample, the second extending direction Dea2 is perpendicular to thefirst stacking direction Dza1. The second magnetic layer 20 a has alength along the second extending direction Dea2 (a second major axislength Lea2). The second magnetic layer 20 a has a length in a direction(direction Dfa2) crossing the first stacking direction Dza1 and crossingthe second extending direction Dea2 (a second minor axis length Lfa2).The second major axis length Lea2 of the second magnetic layer 20 a islonger than the second minor axis length Lfa2 of the second magneticlayer 20 a.

That is, shape anisotropy is provided in the first sensing element unit50 a. In this example, the second extending direction Dea2 runs alongthe first extending direction Dea1. The extending direction of thesecond magnetic layer 20 a (the second extending direction Dea2) isparallel to the extending direction of the first magnetic layer 10 a(the first extending direction Dea1), for example.

The first major axis length Lea1 (the length of the first magnetic layer10 a in the first extending direction Dea1) is not less than 1.5 timesand not more than 3 times the first minor axis length Lfa1 (the lengthof the first magnetic layer 10 a in the direction Dfa1 crossing thefirst stacking direction Dza1 and crossing the first extending directionDea1), for example.

The second major axis length Lea2 (the length of the second magneticlayer 20 a in the second extending direction Dea2) is not less than 1.5times and not more than 3 times the second minor axis length Lfa2 (thelength of the second magnetic layer 20 a in the direction Dfa2 crossingthe first stacking direction Dza1 and crossing the second extendingdirection Dea2), for example.

As shown in FIG. 16B, the third magnetic layer 10 b extends along athird extending direction Deb1. The third extending direction Deb1crosses a second stacking direction Dzb1 from the third magnetic layer10 b toward the fourth magnetic layer 20 b (for example, the Z-axisdirection). In this example, the third extending direction Deb1 isperpendicular to the second stacking direction Dzb1. The third magneticlayer 10 b has a length along the third extending direction Deb1 (athird major axis length Leb1). The third magnetic layer 10 b has alength in the direction (direction Dfb1) crossing the second stackingdirection Dzb1 and crossing the third extending direction Deb1 (a thirdminor axis length Lfb1). The third major axis length Leb1 of the thirdmagnetic layer 10 b is longer than the third minor axis length Lfb1 ofthe third magnetic layer 10 b.

The fourth magnetic layer 20 b extends along a fourth extendingdirection Deb2. The fourth extending direction Deb2 crosses the secondstacking direction Dzb1 from the third magnetic layer 10 b toward thefourth magnetic layer 20 b (for example, the Z-axis direction). In thisexample, the fourth extending direction Deb2 is perpendicular to thesecond stacking direction Dzb1. The fifth magnetic layer 20 b has alength along the fourth extending direction Deb2 (a fourth major axislength Leb2). The fourth magnetic layer 20 b has a length in thedirection (direction Dfb2) crossing the second stacking direction Dzb1and crossing the fourth extending direction Deb2 (a fourth minor axislength Lfb2). The fourth major axis length Leb2 of the fourth magneticlayer 20 b is longer than the fourth minor axis length Lfb2 of thefourth magnetic layer 20 b.

That is, shape anisotropy is provided in the second sensing element unit50 b. In this example, the fourth extending direction Deb2 runs alongthe third extending direction Deb1. The extending direction of thefourth magnetic layer 20 b (the fourth extending direction Deb2) isparallel to the extending direction of the third magnetic layer 10 b(the third extending direction Deb1).

The third major axis length Leb1 (the length of the third magnetic layer10 b in the third extending direction Deb1) is not less than 1.5 timesand not more than 3 times the third minor axis length Lfb1 (the lengthof the third magnetic layer 10 b in the direction Dfb1 crossing thesecond stacking direction Dzb1 and crossing the third extendingdirection Deb1), for example.

The fourth major axis length Leb2 (the length of the fourth magneticlayer 20 b in the fourth extending direction Deb2) is not less than 1.5times and not more than 3 times the fourth minor axis length Lfb2 (thelength of the fourth magnetic layer 20 b in the direction Dfb2 crossingthe second stacking direction Dzb1 and crossing the fourth extendingdirection Deb2), for example.

Each of the first major axis length Lea1, the second major axis lengthLea2, the third major axis length Leb1, and the fourth major axis lengthLeb2 is not less than 0.5 μm and not more than 60 μm, for example.

By providing shape anisotropy in the first sensing element unit 50 a andthe second sensing element unit 50 b and differentiating the directionof shape anisotropy (extending direction), the direction of themagnetization of the reference layer 20 (the second magnetic layer 20 a)of the first sensing element unit 50 a and the direction of themagnetization of the reference layer 20 (the fourth magnetic layer 20 b)of the second sensing element unit 50 b can be differentiated from eachother.

FIG. 17 is a schematic plan view illustrating the inertial sensoraccording to the third embodiment.

In FIG. 17, for easier viewing of the drawing, the boundary betweenportions provided in the connection portion 74 (the first portion 74 a,the second portion 74 b, etc.) is omitted.

As shown in FIG. 17, in the inertial sensor 330 according to theembodiment, a plurality of sensing element units 50 (the first sensingelement unit 50 a, the second sensing element unit 50 b, etc.) areprovided. The plurality of sensing element units 50 are provided alongthe outer edge 72 r of the weight portion 72, for example.

In the first sensing element unit 50 a, the first extending directionDea1 and the second extending direction Dea2 run along the Y-axisdirection, for example.

In the second sensing element unit 50 b, the third extending directionDeb1 and the fourth extending direction Deb2 run along the X-axisdirection, for example.

Thus, the first extending direction Dea1 of the first magnetic layer 10a of the first sensing element unit 50 a crosses the third extendingdirection Deb1 of the third magnetic layer 10 b of the second sensingelement unit 50 b. The second extending direction Dea1 of the secondmagnetic layer 20 a of the first sensing element unit 50 a crosses thefourth extending direction Deb2 of the fourth magnetic layer 20 b of thesecond sensing element unit 50 b.

In the inertial sensor 330, the direction of the magnetization of eachof the plurality of magnetic layers can be controlled using shapeanisotropy. Thereby, a sensing element unit 50 having desiredcharacteristics can be provided in a desired position of the connectionportion 74. Thereby, sensing with higher sensitivity becomes possible.

In this example, the shape of the weight portion 72 when projected ontothe X-Y plane is a circle. The direction 55 of the stress generated whenan acceleration 72 g is applied to the weight portion 72 runs along theradial line with center at the centroid 72 c of the weight portion 72,for example. The extending direction of the magnetic layer is set so asto cross the direction 55 of the stress, for example. The extendingdirection of the magnetic layer crosses the radial line with center atthe centroid 72 c of the weight portion 72, for example. The firstextending direction Dea1 crosses the line passing through the centroid72 c and the first magnetic layer 10 a, for example. The angle betweenthe first extending direction Dea1 and the line passing through thecentroid 72 c and the first magnetic layer 10 a is not less than 70degrees and not more than 110 degrees, for example, and is approximately90 degrees, for example.

The angle from the first direction LN1 to the first extending directionDea1 is substantially equal to the angle from the second direction LN2to the third extending direction Deb1, for example. The differencebetween the angle from the first direction LN1 to the first extendingdirection Dea1 and the angle from the second direction LN2 to the thirdextending direction Deb1 is 10 degrees or less.

FIG. 18A and FIG. 18B are schematic plan views illustrating otherinertial sensors according to the third embodiment.

In the drawings, for easier viewing of the drawings, the boundarybetween portions provided in the connection portion 74 (the firstportion 74 a, the second portion 74 b, etc.) is omitted.

As shown in FIG. 18A and FIG. 18B, also in inertial sensors 330 a and330 b according to the embodiment, a plurality of sensing element units50 (the first sensing element unit 50 a, the second sensing element unit50 b, etc.) are provided.

As shown in FIG. 18A, in the inertial sensor 330 a, the extendingdirection of the magnetic layer is inclined with respect to the radialline with center at the centroid 72 c of the weight portion 72. Theangle between the first extending direction Dea1 and the line passingthrough the centroid 72 c and the first magnetic layer 10 a is largerthan 0 degrees and smaller than 90 degrees, for example. The differencebetween the angle from the first direction LN1 to the first extendingdirection Dea1 and the angle from the second direction LN2 to the thirdextending direction Deb1 is 10 degrees or less, for example.

As shown in FIG. 18B, in the inertial sensor 330 b, the extendingdirection of the magnetic layer runs along the radial line with centerat the centroid 72 c of the weight portion 72. The angle between thefirst extending direction Dea1 and the line passing through the centroid72 c and the first magnetic layer 10 a is plus or minus 5 degrees orless, for example.

Also such inertial sensors can sense acceleration and displacement withhigh sensitivity.

FIG. 19 is a schematic perspective view illustrating another inertialsensor according to the third embodiment.

FIG. 19 illustrates the first sensing element unit 50 a in anotherinertial sensor 330 c according to the embodiment. In FIG. 19, the baseportion 71 and the weight portion 72 are omitted. The base portion 71and the weight portion 72 in the inertial sensor 330 c are similar tothose described in regard to the first and second embodiments, forexample.

As shown in FIG. 19, in the first sensing element unit 50 a, the planarshape of the first magnetic layer 10 a, the second magnetic layer 20 a,and the first intermediate layer 30 a (the shape when projected onto theX-Y plane) is a flat circular shape (including an ellipse). Similarly,also the planar shape of each of the magnetic layers provided in thesecond sensing element unit 50 b may be a flat circular shape.

FIG. 20A and FIG. 20B are schematic perspective views illustratinganother inertial sensor according to the third embodiment.

FIG. 20A illustrates the first sensing element unit 50 a in an inertialsensor 331 according to the embodiment. FIG. 20B illustrates the secondsensing element unit 50 b in the inertial sensor 331. In the drawings,the base portion 71, the weight portion 72, and the connection portion74 are omitted. The base portion 71, the weight portion 72, and theconnection portion 74 in the inertial sensor 331 are similar to thosedescribed in regard to the inertial sensor 330, for example.

As shown in FIG. 20A and FIG. 20B, in this example, the extendingdirection of the magnetization free layer 10 and the extending directionof the reference layer 20 cross each other.

As shown in FIG. 20A, the first magnetic layer 10 a extends along thefirst extending direction Dea1, for example. The second magnetic layer20 a extends along the second extending direction Dea2. The secondextending direction Dea2 crosses the first extending direction Dea1.

As shown in FIG. 20B, the third magnetic layer 10 b extends along thethird extending direction Deb1, for example. The fourth magnetic layer20 b extends along the fourth extending direction Deb2. The fourthextending direction Deb2 crosses the third extending direction Deb1.

That is, in the inertial sensor 331, the direction of the shapeanisotropy provided for the first magnetic layer 10 a is different fromthe direction of the shape anisotropy provided for the second magneticlayer 20 a. The direction of the shape anisotropy provided for the thirdmagnetic layer 10 b is different from the direction of the shapeanisotropy provided for the fourth magnetic layer 20 b. The direction ofthe magnetization based on the shape anisotropy of the first magneticlayer 10 a can be differentiated from the direction of the magnetizationbased on the shape anisotropy of the second magnetic layer 20 a, forexample. The direction of the magnetization based on the shapeanisotropy of the third magnetic layer 10 b can be differentiated fromthe direction of the magnetization based on the shape anisotropy of thefourth magnetic layer 20 b, for example. Thereby, a sensing element unit50 having desired magnetization directions is obtained. Sensing withhigher sensitivity becomes possible.

FIG. 21 is a schematic plan view illustrating another inertial sensoraccording to the third embodiment.

FIG. 21 is a plan view of the inertial sensor 331 according to theembodiment. In FIG. 21, for easier viewing of the drawing, the boundarybetween portions provided in the connection portion 74 (the firstportion 74 a, the second portion 74 b, etc.) is omitted.

As shown in FIG. 21, a plurality of sensing element units 50 (the firstsensing element unit 50 a, the second sensing element unit 50 b, etc.)are provided along the outer edge 72 r of the weight portion 72.

In this example, when projected onto the X-Y plane, the straight line 56a passing through the centroid 7 c of the weight portion 72 and thefirst sensing element unit 50 a, and the first extending direction Dea1of the first magnetic layer 10 a cross each other. The straight line 56a and the second extending direction Dea1 of the second magnetic layer20 a cross each other. In this example, the angle between the straightline 56 a and the first extending direction Dea1 is equal to the anglebetween the straight line 56 a and the second extending direction Dea1.

In this example, when projected onto the X-Y plane, the straight line 56b passing through the centroid 7 c of the weight portion 72 and thesecond sensing element unit 50 b, and the third extending direction Deb1of the third magnetic layer 10 b cross each other. The straight line 56b and the fourth extending direction Deb2 of the fourth magnetic layer20 b cross each other. In this example, the angle between the straightline 56 b and the third extending direction Deb1 is equal to the anglebetween the straight line 56 b and the fourth extending direction Deb2.

The inertial sensor 331 enables sensing with higher sensitivity.

In the case where the extending directions of the magnetic layersincluded in the sensing element unit 50 are different, the angle betweenextending directions is arbitrary. The angle between the straight linepassing through the centroid 72 c of the weight portion 72 and thesensing element unit 50 and the extending direction of the magneticlayer is arbitrary.

FIG. 22A and FIG. 22B are schematic plan views illustrating otherinertial sensors according to the third embodiment.

The drawings illustrate configurations of the sensing element unit 50(the first sensing element unit 50 a) used for the inertial sensor 331.In the drawings, the intermediate layer 30 (the first intermediate layer30 a) is omitted. The drawings illustrate planar shapes of the firstmagnetic layer 10 a and the second magnetic layer 20 a.

In the example shown in FIG. 22A, the planar shape of each of the firstmagnetic layer 10 a and the second magnetic layer 20 a is a rectangle.In this case, the first major axis length Lea1 corresponds to the lengthof the long side of the rectangle. The first minor axis length Lfa1corresponds to the length of the short side of the rectangle. The secondmajor axis length Lea2 corresponds to the length of the long side of therectangle. The second minor axis length Lfa2 corresponds to the lengthof the short side of the rectangle.

In the example shown in FIG. 22B, the planar shape of each of the firstmagnetic layer 10 a and the second magnetic layer 20 a is a flatcircular shape (including an ellipse). In this case, the first majoraxis length Lea1 corresponds to the length of the major axis of the flatcircle. The first minor axis length Lfa1 corresponds to the length ofthe minor axis of the flat circle The second major axis length Lea2corresponds to the length of the major axis of the flat circle. Thesecond minor axis length Lfa2 corresponds to the length of the minoraxis of the flat circle.

In the embodiment, the planar shape of the magnetic layer may bevariously modified.

Fourth Embodiment

FIG. 23 is a schematic perspective view illustrating an inertial sensoraccording to a fourth embodiment.

As shown in FIG. 23, in an inertial sensor 340 according to theembodiment, a plurality of sensing element units 50 (a plurality offirst sensing element units 50 a) are provided in the first portion 74 aof the connection portion 74. In this example, a part of the pluralityof first sensing element units 50 a are aligned along a direction alongthe outer edge 72 r of the weight portion 72. Another part of theplurality of first sensing element units 50 a are aligned along thedirection of the radial straight line running from the centroid 72 c ofthe weight portion 72 toward the outer edge 72 r (for example, the firstdirection LN1).

In this example, a plurality of second sensing element units 50 b areprovided in the second portion 74 b of the connection portion 74. Inthis example, a part of the plurality of second sensing element units 50b are aligned along a direction along the outer edge 72 r of the weightportion 72. Another part of the plurality of second sensing elementunits 50 b are aligned along the direction of the radial straight linerunning from the centroid 72 c of the weight portion 72 toward the outeredge 72 r (for example, the second direction LN2).

When an acceleration 72 g is applied, a strain is generated in each ofthe first portion 74 a and the second portion 74 b of the connectionportion 74. By providing a plurality of first sensing element units 50 ain the first portion 74 a in which a strain in the same direction isgenerated, sensitivity is improved more. By providing a plurality ofsecond sensing element units 50 b in the second portion 74 b in which astrain in the same direction is generated, sensitivity is improved more.The plurality of sensing element units 50 provided may be connected toone another in series or in parallel.

FIG. 24A to FIG. 24C are schematic diagrams illustrating inertialsensors according to the fourth embodiment.

The drawings show examples of the connection state of a plurality ofsensing element units 50 (first sensing element units 50 a).

As shown in FIG. 24A, in an inertial sensor 341 a according to theembodiment, a plurality of sensing element units 50 are electricallyconnected in series. A plurality of first sensing element units 50 a areprovided on the first portion 74 a, for example. At least two of theplurality of first sensing element units 50 a are electrically connectedin series.

When the number of sensing element units 50 connected in series isdenoted by N, the electric signal obtained is N times of that when thenumber of sensing element units 50 is one. On the other hand, thethermal noise and the Schottky noise are N^(1/2) times. That is, the S/Nratio (signal-noise ratio; SNR) is N^(1/2) times. By increasing thenumber N of sensing element units 50 connected in series, the S/N ratiocan be improved without increasing the size of the connection portion74.

The change in electric resistance R with respect to the acceleration 72g (for example, polarity) is similar between first sensing element units50 a provided in the first portion 74 a where the first sensing elementunit 50 a is provided, for example. Therefore, it is possible to sum upthe signals of the plurality of first sensing element units 50 a.

The bias voltage applied to one sensing element unit 50 is not less than50 millivolts (mV) and not more than 150 mV, for example. When N sensingelement units 50 are connected in series, the bias voltage is not lessthan 50 mV×N and not more than 150 mV×N. When the number N of sensingelement units 50 connected in series is 25, the bias voltage is not lessthan 1 V and not more than 3.75 V, for example.

When the value of the bias voltage is 1 V or more, the design of anelectric circuit that processes the electric signal obtained from thesensing element unit 50 is easy, and this is preferable in practicalterms. A plurality of sensing element units 50 from which electricsignals with the same polarity are obtained when pressure is producedare provided, for example. By connecting these sensing elements inseries, the S/N ratio can be improved as mentioned above.

Bias voltages (inter-terminal voltages) exceeding 10 V are notpreferable in the electric circuit that processes the electric signalobtained from the sensing element unit 50. In the embodiment, the numberN of sensing element units 50 connected in series and the bias voltageare set so that an appropriate voltage range is obtained.

The voltage when the plurality of sensing element units 50 areelectrically connected in series is preferably not less than 1 V and notmore than 10 V, for example. The voltage applied between the terminalsof the two ends of the plurality of sensing element units 50 (the firstsensing element units 50 a) electrically connected in series (betweenthe terminal of one end and the terminal of the other end) is not lessthan 1 V and not more than 10 V, for example.

To generate this voltage, when the bias voltage applied to one sensingelement 50 is 50 mV, the number N of sensing element units 50 connectedin series is preferably not less than 20 and not more than 200. When thebias voltage applied to one sensing element unit 50 is 150 mV, thenumber N of sensing element units 50 (first sensing element units 50 a)connected in series is preferably not less than 7 and not more than 66.

As shown in FIG. 24B, in an inertial sensor 341 b according to theembodiment, a plurality of sensing element units 50 (first sensingelement units 50 a) are electrically connected in parallel. In theembodiment, at least part of a plurality of sensing element units 50 maybe electrically connected in parallel.

As shown in FIG. 24C, in an inertial sensor 341 c according to theembodiment, a plurality of sensing element units 50 (first sensingelement units 50 a) are connected so as to form a Wheatstone bridgecircuit. Thereby, the temperature compensation of detectedcharacteristics can be made, for example.

The embodiment can provide an inertial sensor that senses acceleration,displacement, etc. with high sensitivity.

Hereinabove, embodiments of the invention are described with referenceto specific examples. However, the embodiment of the invention is notlimited to these specific examples. For example, one skilled in the artmay appropriately select specific configurations of components ofinertial sensors such as base portions, weight portions, connectionportions, sensing element units, magnetic layers, and intermediatelayers from known art and similarly practice the invention. Suchpractice is included in the scope of the invention to the extent thatsimilar effects thereto are obtained.

Further, any two or more components of the specific examples may becombined within the extent of technical feasibility; and suchcombinations are included in the scope of the invention to the extentthat the spirit of the invention is included.

Moreover, all inertial sensors practicable by an appropriate designmodification by one skilled in the art based on the inertial sensorsdescribed above as embodiments of the invention also are within thescope of the invention to the extent that the spirit of the invention isincluded.

Various other variations and modifications can be conceived by thoseskilled in the art within the spirit of the invention, and it isunderstood that such variations and modifications are also encompassedwithin the scope of the invention.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A sensor comprising: a first member; a secondmember connected with the first member, the second member beingdeformable; a third member connected with the second member, the secondmember being provided between the first member and the third member; afirst sensing element unit provided at a first portion of the secondmember, the first sensing element unit being provided between the firstmember and the third member in a first direction along an outer edge ofthe second member, the first sensing element including a first magneticlayer, a second magnetic layer, and a first intermediate layer, thefirst intermediate layer being provided between the first magnetic layerand the second magnetic layer and being nonmagnetic; and a secondsensing element unit provided at a second portion of the second member,the second sensing element unit being provided between the first memberand the third member in the first direction, the second sensing elementincluding a third magnetic layer, a fourth magnetic layer, and a secondintermediate layer, the second intermediate layer being provided betweenthe third magnetic layer and the fourth magnetic layer and beingnonmagnetic, wherein a length of the second member in the firstdirection is shorter than a length of the third member in the firstdirection, wherein the direction from a part of the first memberconnected with the second member toward a part of the second memberconnected with the third member is along the first direction.
 2. Thesensor according to claim 1, wherein a second direction from the firstsensing element unit toward the second sensing element unit crosses thefirst direction.
 3. The sensor according to claim 1, wherein the firstsensing element unit and the second sensing element unit areelectrically connected in series.
 4. The sensor according to claim 1,further comprising: a third sensing element unit provided at a thirdportion of the second member and including a fifth magnetic layer, asixth magnetic layer, and a third intermediate layer, the thirdintermediate layer being provided between the fifth magnetic layer andthe sixth magnetic layer and being nonmagnetic, and a direction from thefirst sensing element unit toward the third sensing element unit isalong the first direction.
 5. The sensor according to claim 1, whereinthe second member is configured to be deformed in accordance with achange in a relative position of the third member with respect to aposition of the first member.
 6. The sensor according to claim 1,wherein at least a part of the first magnetic layer includes iron andhas an amorphous structure.
 7. The sensor according to claim 6, whereinthe at least the part of the first magnetic layer includes boron.
 8. Thesensor according to claim 1, wherein the second member includes a firstside extending along the first direction.
 9. The sensor according toclaim 8, wherein the second member further includes a second sideextending along the first direction.
 10. The sensor according to claim1, wherein a length of the second member in a second direction crossingthe first direction is shorter than a length of the third member in thesecond direction.